For those unfortunate enough to have lost vision because of accident or diseases such as retinitis pigmentosa, macular degeneration, or glaucoma, restoration of function would mean a tremendous increase in the quality of life.
Existing approaches for replacement of visual function vary widely, e.g., extracranial devices, intra-ocular devices, and intracranial devices.
Extracranial approaches replace the sense of vision by mapping to another sense, such as auditory or tactile, or by electrically stimulating visually-relevant structures. All of these approaches suffer because they only provide a surrogate sensation and do not create visual perception. The shortcomings, which include poor spatial and temporal resolution, cumbersome equipment, and objectionable side-effects, have prevented such approaches from gaining acceptance beyond that of parlor-room curiosity.
Others have tried to restore visual perceptions by stimulating the outer (epi-) or inner (sub-) structures of the retina, by adjusting the geometry of the retina to optimize remaining function, or by directly stimulating the optic nerve. The epi- and sub-retinal approaches place electronic devices at the outer or inner surfaces of the retina, respectively. While initial results from these efforts are interesting, the retina is a delicate structure that does not take well to manipulation, and long-term stability remains a serious concern. Further, for epi-retinal devices in particular, the architecture of the outer retina is not ideal because stimulating the ganglion cells at a given point will unavoidably stimulate axons from retinotopically distant cells, which will make it impossible to create detailed visual percepts. For the subretinal devices under investigation, limitations on the amount of optically-deliverable power preclude operation at all but the highest levels of illumination.
Another approach seeks to deliver electrical stimulation directly to the primary visual cortex and entirely bypasses the early stages of the visual system. However, the complexity of cellular response in the primary visual cortex, and the relative inaccessibility of the important foveal representation prevent the primary visual cortex from being a good target for an implant. Therefore, creation of an effective synthetic visual experience of more than passing detail from an implant in the cortex is quite difficult.
It is an object of the present invention to provide a visual prosthesis and methods of creating visual perceptions in a mammal that reduce or wholly overcome some or all of the difficulties inherent in prior known devices. Particular objects and advantages of the invention will be apparent to those skilled in the art, in view of the following disclosure of the invention and detailed description of certain preferred embodiments. These and other objects are satisfied by the methods and products disclosed herein.